#include <iostream>
#include <string>

using namespace std;

class  basic{
public:
    virtual double add() = 0;

public:
};

class f_child: public basic{
public:
    f_child(double f):_f(f){}

    double add()override{
        return _i + _f;
    }

private:
    int _i = 10;
    double _f;
};

struct basic_st
{
    int _it;
};

struct st_child: public basic_st
{
    int _ist;
};


int main(){
    basic *b = new f_child(5.9);

    cout << "number = " << b->add() << endl;
}